Electroluminescent panel driver

ABSTRACT

1. A driver of the character described operable from power supply and control voltages below the firing potential of gas filled tubes, said driver comprising: a source of alternating electric current; a voltage step-up transformer having primary and secondary windings; solid state means connected in series with the primary winding of said transformer and with saId source of alternating current for half-wave rectifying and for controllably interrupting half-wave current flow through said primary winding; a source of direct current control signals; a first transistor connected to said source of control signals and having conductive and nonconductive conditions in response to changes in said control signals, said first transistor being connected to said solid-state means and operative in one of said conditions to cause said solid-state means to interrupt said half-wave current flow through said primary winding, and in the other of said conditions to cause said solid-state means to permit said half-wave current flow whereby said secondary winding provides an alternating current output of higher voltage than said alternating current source and only in response to a predetermined voltage signal form said control signal source; said solid-state means comprising a rectifier diode, and a second transistor having base, emitter and collector connections, said primary winding being connected in series with said diode and said source of alternating current through said emitter and collector connections of said second transistor; said first transistor having emitter and collector connections connected in series with said diode and said alternating current source, one of said emitter and collector connections of said first transistor being connected to the base of said second transistor, and said first transistor having a base connection coupled to said control signal source.

United States Patent i721 inventor Wolfgang Merel Cedar Grove, NJ. l2l| Appl No 353,307 [22] Filed Mar. [9, I964 [45] Patented Sept. 7, I971 Assignee The United States of America as represented by the Secretary ol the Navy {54] ELECTROLUMINESCENT PANEL DRIVER 1 Claim, 3 Drawing Figs.

[52] Utsuclem r. 307/239, 307/307 (51] Int, Cl "03k 3/26, H03k 19/08 {50] Field of Search 307/885,

215', 328/l27, 84, ZIO; 3 l5/l69TV, 209 CD OTHER REFERENCES Applications and Circuit Design Notes, Solid State Products, lnc., Bulletin D420- 02, Aug. 1959, page 27. Wave Fonns" by Chance et al., Vol. l9, page 18, Radiation Laboratory Series, QC 60I C5 4- 49 Primary Examiner-Arthur Gauss Assistant Examiner-B. P, Davis Attorneys-R l, Tompkins, J. W Pcase and H A, David CLAIM: IV A driver of the character described operable from power supply and control voltages below the firing potential of gas filled tubes, said driver comprising: a source of alternating electric current; a voltage step-up transformer having primary and secondary windings; solid state means connected in series with the primary winding of said transformer and with said source of alternating current for half-wave rectifying and for eontrollably interrupting half-wave current flow through said primary winding; a source of direct current control signals; a first transistor connected to said source of control signals and having conductive and nonconductive conditions in response to changes in said control signals, said first transistor being connected to said solid-state means and operative in one of said conditions to cause said solid-state means to interrupt said half-wave current flow through said primary winding, and in the other of said conditionsto cause said solid-state means to permit said ha1f-wave current flow whereby said secondary winding provides an alternating current output of higher voltage than said alternating current source and only in response to a predetermined voltage signal form said control signal source; said solid-state means comprising a rectifier diode, and a second transistor having base, emitter and collector connections, said primary winding being connected in series with said diode and said source of alternating current through said emitter and collector connections of said second transistor; said first transistor having emitter and collector connections connected in series with said diode and said alternating current source, one of said emitter and collector connections of said first transistor being connected to the base of said second transistor, and said first transistor having a base connection coupled to said control signal source.

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ELECTROLUMINESCENT PANEL DRIVER This invention relates to a pulse shaper, and more particularly to a controllable electroluminescent driver circuit.

Various circuits have been devised to control the passage of AC power to an electroluminescent load. A typical AC switch is that which utilizes two high voltage silicon controlled rectifiers, referred to as SCRs," in back-to-back relationship with control isolation. Also various circuits were devised which utilized two high voltage switching transistors in series, or two high voltage switching transistors in parallel. Such circuitry, in providing the same function, is more complex than the instant invention.

Therefore, one of the objects of the invention, is to provide a lower cost and less complex driver circuit.

A further object of the invention, is to provide means to simply control an AC source.

Another object of the invention is to provide a high voltage logic controllable means to control an AC source.

Basically, one embodiment of the invention comprises; an AC input source, a diode element, a step-up transformer, and a controllable switch, all in series relationships. The switch is controlled by logic circuitry, and when the switch is commanded on," and is thereby conducting, a current pulse will flow through the series when the polarity of the input signal is such as to pass through the diode. Operation of the circuit in this manner, half-wave" mode, allows "Class B operation of the driver elements lowering dissipation and simplifying the circuitry.

An object of the invention therefore, is to provide an improved driver circuit operable in the "Class B" mode.

Another object of the invention is to provide a simple driver circuit, which is operable in the "Class B" mode.

A still further object of this invention is to provide a circuit, controllable by digital logic, to drive an isolated high voltage electroluminescent panel device.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a schematic diagram of one embodiment of the invention',

FIG. 2 is a schematic diagram of another embodiment of the invention; and

FIG. 3 is a series of waveforms useful in explaining the operation of the embodiments illustrated in FIGS. 1 and 2.

Referring to FIG. 1, the invention broadly comprises a unidirectional energy transfer means, which is coupled to a bipolar high frequency signal source, a step-up transformer means, and a switching means. Each of said elements are connected in a series relationship with one another. Additionally, there is provided a control means for controlling the state of the switching means. The switching means is either in an on" or ofi state, and includes a control element. Additionally, a logic signal source is provided which is used for actuating the control means. More specifically, the invention includes a bipolar signal source of a high frequency as for example, a 100 kilocycles sinusoidal voltage at approximately 28 volts peak to peak. This bipolar signal source 10, is coupled over line 7, to terminal 1, and then cathode 9 of diode D, element ll. The anode 12 of said diode 1], is then coupled to one end of resistor R,, element 13. The anode 12, of diode 11, is also connected to one end of the primary of the step-up transformer T, element 15. The other end of the primary of the transformer 15, is coupled directly to the collector of transistor 0,, element 17. The emitter of transistor 0,, element 17, is connected through resistor R element I9, to ground at terminals 3 and 4. The secondary of transformer T,, element I5, is connected directly to the output terminals 5, and 6, coupling the resulting output voltage to its intended load. The control means for controlling the state of transistor 0,, element 17, includes resistor R,, element I3, one end of which is coupled to the anode 12 of diode 11, the other end of which is coupled to the collector of transistor 0,, element 21, which has its emitter element coupled through resistor R,, element 27, to terminals 3 and 4, ground. Additionally, there is coupled between the transistors base to emitter voltage within certain necessary limits. Additionally, there is coupled between the base of transistor 21, and terminal 2, resistor R element 25, which provides signal current limiting for the transistor 0,, element 21. Resistor R,, element I3, as used in this control section is used to limit the current flowing through transistor 0,, element 21. Resistors I3, 23, 25 and resistor R,, element 27, are used for establishing operating conditions dur ing on" commands. Resistor R element 23, described in connection with the series circuit which including transistor 0,, element 17 is used as a current feedback and current limiting for transistor 0,, element 17. The control means is connected to a command signal source 20, negative logic in this specific embodiment over line 29, to terminal 2. The other end of the command signal source 20, is coupled to ground. Referring now to FIG. 1 and the waveforms shown in FIG. 3, the input bipolar high frequency signal, (KC, approximately 28 volts peak-to-peak) represented by curve A is applied over line 7 to terminal 1. Only those portions of said signal having a negative polarity are capable of passing through diode D,, element 11, and the other series elements, the primary of transformer T, element l5, and the switching means 0,, element 17 to ground. Additionally, the negative portions of such signal represented by curve will only generate current through the primary of transformer 15, and transistor switch 0,, element 17, when the transistor switch 0,, element 17, is conducting, that is, when it is in the on state. This is observed, by referring to the command signal 20, represented by curve B wherein during the first cycle of operation of the driver the command signal represented by curve B," has a voltage magnitude of zero volts, which are insufficient to allow transistor 0,, element 21, to conduct, and hence transistor 0,, element 17, is also nonconducting. The result is that there is no current flowing through the primary of transformer T,, element 15. This is easily seen by referring to the curve "C" and D' which represent the current through the primary transformer 15, and the output voltage across terminals 5 and 6 respectively, during the same time-sequence; i.e., the first cycle of input wave, represented by curve A. After the first cycle, the command signal 20, represented by curve D," having now changed to a minus 10 volts, a suffcient value to bias transistor 0,, element 21, to conduction. This will result in transistor 0,, element 21, conducting and thereby switching transistor 0,, element 17, to an "on" state thereby allowing current to flow therethrough and the rest of the series circuit. During such "on cycle, whenever a negative bipolar input signal from source 10, is applied at terminal 1, current will flow through diode 11 through the primary of transformer 15, and through the on" transistor switch 0,, element 17. This will result in a current series of pulses, in a negative direction as represented by curve "C." Each of such current pulses initially starts at a zero value due to the inherent current pulse characteristics of an inductor. The magnitude of the current pulse characteristics of an inductor. The magnitude of the current will increase due to the fact that the negative portion of the input signal, is increasing represented by curve A, during such time and will eventually level off, and start, to return to zero during the positive cycle of the bipolar input signal, represented by curve "A, which is not allowed to pass through the diode ll, nor through the overall series circuit. However, now referring specifically to the out put voltage, resultant at output terminals 5 and 6, represented by curve "D" it is seen that there is a sinusoidal" voltage resulting during such on sequence. The waveform of this output voltage, represented by curve D," is of course, ideally a differential of the current, represented by curve C through the transformer 15, as a function of time. The amplitude of the output voltage is approximately 1,000 volts peak-to-peak in this specific embodiment. due to the turn ratio of the transformer.

in summary, therefore, it is seen that there is provided an appreciable step-up of an input high frequency input voltage signal by said driver circuit, which operates in the half-wave mode. By operating in class 8" operation, half-wave mode, the circuitry is simplified, single ended, and the dissipation is lowered. A small positive bias, (not shown) in series with the command signal 20, can be used to assure that the output voltage will drop to less than certain value after an of! command. The necessitation of using this particular inventive form of driver is due to the high cost and complexity encountered by other means. This circuit is particularly adaptable for use in a driver for providing high voltage, high frequency, low current needed by electroluminescent panels. This is described in detail in an article by the inventor, Mr. W. Merel, and by Mr. H. Barkan, in an article entitled "Computer Compatible Electroluminescent Techniques For The Achievement Of Wide Angle Visual Display, published in the I963 IEEE international Convention Record Part 4. This driver has utility as a pulse shaper and its utility is not solely restricted to such aforementioned environment. Referring now to FIG. 2, which is another embodiment of the inventive which utilizes negative logic as does the inventive embodiment illustrated in FIG. 1. This embodiment basically comprises; an input signal source 30 of a high frequency in this case a specific embodiment 30 volts peak-to-peak at 100 kc. and a step-up transformer which is coupled, at one end, to said input signal source, and a controllable unidirectional switch means, which is coupled to the other side of said transformer. Such switching means 31, which has an element 33, which is used to control its state, on or "off," is controlled by a controllable firing means 35, which is capable of changing the state of the switching means 31. This controllable firing means 35, is itself controlled by a negative logic signal source 37, and in this embodiment by a negative 10 volt pulse signal. More specifically, the invention includes an input signal source 30, coupled to terminals l and 2. A transformer 39, having one end of its primary coupled to terminal 1. The other end of the primary of said transformer 39, is coupled to one end of the switch means 3|, which in this embodiment is a silicon controlled rectifier means. The other end of said silicon rectifier means 31 is coupled directly to ground 3. The silicon control means 31 has a control element or firing element 33, and is controlled by a transistor 35, which has its collector coupled through a diode 41, to said control element 33. The control transistor 35, is gated on and by a command signal source 37. The output of said driver is taken off the secondary output of said transformer 39.

The device operates in a similar manner as the circuit illustrated in FIG. 1. Only when the switching means 31, is allowed to conduct and when the input signal source 30, is of a particular polarity, positive in this case, any current flow through the transformer 39 which is in series with the switch means 31. When such positive portion of the signal is allowed to flow through the primary of said transformer 39, the current resulting therefrom will induce a voltage at the output of the transformer 39, which will be of a sinusoidal waveform, and

stepped-up considerably, depending upon the turns ratio of the transformer 39. More specifically when there is a zero command signal, applied at the input terminal 2, the input transistor 34, is biased on, that is, it is conducting. This keeps the silicon control rectifier turned off, preventing any current flow through the primary of transformer 39, connected in series therewith. When the command signal changes to a sufficiently negative value, the input transistor 35, is turned off, turning the SCR 31, on," thereby allowing current to flow through the primary of the transformer 39, in series therewith. By using this particular form of circuitry, diode D,, element ii, and control transistor 0,, element 21, and its associated circuitry, of the embodiment illustrated by FIG. 1,

is eliminated.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the ap pended claims the invention may be practiced otherwise than as specifically describedv What is claimed is:

l. A driver of the character described operable from power supply and control voltages below the firing potential of gas filled tubes, said driver comprising:

a source of alternating electric current;

a voltage step-up transformer having primary and secondary windings;

solid-state means connected in series with the primary winding of said transformer and with said source of alternating current for half-wave rectifying and for controllably interrupting half-wave current flow through said primary winding;

a source of direct current control signals;

a first transistor connected to said source of control signals and having conductive and nonconductive conditions in response to changes in said control signals, said first transistor being connected to said solid-state means and operative in one of said conditions to cause said solidstate means to interrupt said half-wave current fiow through said primary winding, and in the other of said conditions to cause said solid-state means to permit said half-wave current flow whereby said secondary winding provides an alternating current output of higher voltage than said alternating current source and only in response to a predetermined voltage signal from said control signal source;

said solid-state means comprising a rectifier diode, and a second transistor having base, emitter and collector connections, said primary winding being connected in series with said diode and said source of alternating current through said emitter and collector connections of said second transistors;

said first transistor having emitter and collector connections connected in series with said diodes and said alternating current source, one of said emitter and collector connections of said first transistor being connected to the base of said second transistor, and said first transistor having a base connection coupled to said control signal source. 

1. A driver of the character described operable from power supply and control voltages below the firing potential of gas filled tubes, said driver comprising: a source of alternating electric current; a voltage step-up transformer having primary and secondary windings; solid-state means connected in series with the primary winding of said transformer and with said source of alternating current for half-wave rectifying and for controllably interrupting half-wave current flow through said primary winding; a source of direct current control signals; a first transistor connected to said source of control signals and having conductive and nonconductive conditions in response to changes in said control signals, said first transistor being connected to said solid-state means and operative in one of said conditions to cause said solid-state means to interrupt said half-wave current flow through said primary winding, and in the other of said conditions to cause said solid-state means to permit said half-wave current flow whereby said secondary winding provides an alternating current output of higher voltage than said alternating current source and only in response to a predetermined voltage signal from said control signal source; said solid-state means comprising a rectifier diode, and a second transistor having base, emitter and collector connections, said primary winding being connected in series with said diode and said source of alternating current through said emitter and collector connections of said second transistors; said first transistor having emitter and collector connections connected in series with said diodes and said alternating current source, one of said emitter and collector connections of said first transistor being connected to the base of said second transistor, and said first transistor having a base connection coupled to said control signal source. 